1. Field of the Invention
The present invention relates generally to the field of two-wire, high frequency dimmable electronic ballasts for powering gas discharge lamps and the like and, more particularly, to a ballast system capable of being remotely addressed for light level control without the need of any additional wires to the main power supply leads to the ballast.
2. Description of the Prior Art
Solid-state electronic dimming ballast for supplying power to fluorescent or other types of gas discharge lamps are known in the prior art. These ballasts provide the same primary function as the conventional 50-60 hz heavy core-coil ballasts which have been used for many years. The solid-state ballasts normally convert conventional 50-60 hz AC to DC and then invert the DC to drive the lamps at a much higher frequency. That frequency generally is in the 10 to 50 KHz range. It has been found that flourescent lamps, for example, which are operated at these higher frequencies have a much higher energy efficiency than those operated at 60 hz and they exhibit lower power losses and longer lamp life. In addition, at high frequencies, annoying flickering and ballast hum associated with 50 or 60 Hertz systems are substantially reduced.
Because of the increase in the cost of electric power generally, there exists a rising concern for achieving higher energy efficiency in electric lighting. Most large commercial and public buildings employ numerous, sometimes thousands, of high energy discharge lamps such as fluorescent lamps to provide lighting for large square footage areas, offices and the like. More and more of these buildings are utilizing remote, centralized systems for controlling individual remote functions throughout the building such as the temperature of individual offices or rooms, locking and unlocking of numerous doors, intrusion detection, detection of fire and smoke, and such other functions as controlling individual loads during power load-shedding intervals. In such systems, normally, a centralized control station which may include a computer or other data processing system is utilized to address remote locations by means of a signalling system utilizing radio frequency, ultrasonics or a powerline carrier communication system which uses the existing building electrical network.
Insofar as application of such systems to electronic dimming ballasts is concerned, the prior art has normally depended on individual SCR controllers to modulate the average voltage supplied from the main powerline source to each individual ballast to, in turn, modulate the lamp output. Alternate systems have utilized additional low voltage wiring, for example, to supply a control signal to the ballast to turn it on and off and for dimming. Addressing could be accomplished by the SCR-controller or by the separately run control wires.
The problems associated with addressing a large number of such systems in an installation without the necessity of adding additional wiring or other control means have not been solved by the prior art. Thus, the need for a remotely addressing control system which does not require additional wiring and can achieve the desired control inexpensively has existed for some time.